1. Field of the Invention
The invention relates to a liquid crystal display device, and manufacturing method for printing a color filter and contact material onto a substrate which reduces manufacturing process and cost.
2. Description of the Related Art
Liquid crystal display devices are being actively developed due to their advantages such as small volume, light weight, little power consumption and large screen compared to typical cathode ray tubes (“CRTs”) used as monitors, TVs (televisions), and the like. Recently, there has been a step up to develop technology for increasing display size and reducing cost of LCDs. In particular, technologies for reducing costs are important in terms of achieving general acceptance of color liquid crystal displays. A method of manufacturing color filters has been proposed as one such cost reduction technology, and is described below.
A method of forming color filter such as R (Red), G (Green), and B (Blue) has been photolithography on a glass substrate. However, drawbacks of photolithography processes include the high cost of equipment needed for coating, exposure, development, and so on, as well as low utilization efficiency of the principal materials of the RGB color filters. Consequently, ink-jet processes and printing processes have been proposed as color filter production methods which can replace the photolithography process.
Ink-jet processes have the advantage that alignment of the various color filter patterns can be accomplished through program control. However, susceptibility to nozzle clogging and slow processing speed are potential issues in terms of mass production.
Printing processes are already in use for certain products. Depending on the type of printing plate used or difference in the printing mechanism, printing processes are classified as gravure printing, anastatic printing, planographic printing, reverse printing, and so on. However, in consideration of throughput and the pattern dimensions required for color filters, gravure printing is perhaps best adapted as a color filter production process.
By way of illustration, a color filter production process employing a conventional gravure printing process will be described in detail. FIGS. 1A to 1D are outline diagrams illustrating the manufacturing flow of a conventional color filter substrate, where FIG. 1A is a cross-sectional view of the gravure printing plate being filled with colored ink and a doctoring blade, FIG. 1B is a cross-sectional view after the blanket has received the colored ink, FIG. 1C is a cross-sectional view after transfer of the colored ink to the transparent substrate and FIGS. 1D and 1E are cross-sectional views of the substrate being pressed by a press sheet and pressing apparatus including press roller or press plate, respectively.
As depicted in FIG. 1A, a gravure printing plate 500 including recesses 560 formed thereon is positioned on a stage 10, ink 600 is placed on the edge of the gravure printing plate 500, and a blade 510 is pressed against the gravure printing plate 500 and swept thereover so as to wipe it, thereby filling the recesses 560 with the ink 600. Subsequently, as depicted in FIG. 1B, a blanket 520 is pressed against the gravure printing plate 500 and turned, whereby the ink 600 filling the recesses 560 is accepted onto the blanket 520. The ink 600 is accepted onto the surface of the blanket 520. In consideration of the fact that the ink becomes split when the ink is accepted onto the blanket 520, the depth of the recesses 560 is designed so as to make allowance for the ink left at the bottom of the recesses 560.
Next, as depicted in FIG. 1C, a transparent substrate 110 is placed on the stage 10, and the ink 602 that has been picked up on the blanket 520 is transferred to the transparent substrate 110. The above operation is repeated three times to produce an RGB 3-color filter. Next, as depicted in FIG. 1D and FIG. 1E, a press roller 540 covered with a press sheet 550, or press plate 570 covered with a press sheet 550 press the transferred ink to fill the vacant space.
A plurality of thin film transistor arrays is disposed on a first substrate and a plurality of color filters is disposed on a second substrate in a conventional liquid crystal display. However, the difficulty in controlling the width of the transferred ink in the forming of the color filter during a conventional gravure printing process may cause many drawbacks, such as poor accuracy in alignment of the first substrate and the second substrate. If a miss-alignment occurs, the image quality of the display becomes poor. Additionally, a contact hole in the color filter is required for disposing a conductive contact element to connect a source electrode and a pixel electrode to each other. It is difficult to form the contact hole after a gravure printing method because of residuals.
According to FIGS. 2A to 2C, ink transferred to the substrate has a substantially dome shape. FIG. 2A shows a plan view of the dome-shaped ink transferred to the substrate, FIG. 2B shows a cross-sectional view along line A-A′ of FIG. 1 of the dome-shaped ink transferred to the substrate and forming a printed RGB pattern (600G, 600B, 600R), FIG. 2C shows a color filter (600GP, 600BP, 600RP) formed from the printed RGB pattern (600G, 600B, 600R).
Since the ink is transferred directly from the gravure printing plate onto the transparent substrate, a drawback may arise since the three transferred ink patterns have poor dimensional accuracy.
Specifically, when the gravure printing plate including recesses filled with ink is directly pressed against the glass substrate for ink to be transferred thereto, the upper portions of the recesses become splayed by the pressing force, making it difficult to control the width of the transferred ink.
In FIG. 2C, the color filter (600GP, 600BP, 600RP) does not include a contact hole for a conductive contact element to connect a source electrode and a pixel electrode to each other, as a result of the forming of the color filter (600GP, 600BP, 600RP) from the printed RGB pattern (600G, 600B, 600R) during only a conventional gravure printing process. Therefore, cost and time is increased since the contact hole must be formed after the conventional gravure printing method.
Additionally, since the dimensions of the color filter (600GP, 600BP, 600RP) from the printed RGB pattern (600G, 600B, 600R) are not bounded by any control feature, and are defined only by the pressing of the unrestricted RGB pattern (600G, 600B, 600R) during the conventional gravure printing method, a poor accuracy in alignment of the first substrate and the second substrate may be created.
Splitting of the ink during ink transfer can be prevented and the accuracy of the ink pattern improved by filling the recesses of the gravure printing plate with photosensitive ink and then exposing the ink for curing. The accuracy of the ink pattern may be improved further by accelerating the setting rate via a heat treatment or the like.